The investigator measures the muscle soreness and muscle stiffness before the patients starts their prescribed treatment with amitriptyline - and again after they have reached their optimal dosage of amitriptyline.

The investigator measures the muscle soreness and muscle stiffness once.

The investigator recruits patients who have already discussed and agreed to the amitriptyline treatment with their physician. The patients start the treatment after the investigator have measured them once.

The soreness of the muscle is reported by the patient on a scale from 0-3 (0= no pain, 1= mild pain, 2= moderate pain and 3= severe pain) when pressure is applied at eight different locations on both sides of the face and neck (m. masseter, m. frontalis, m. pterygoideus lateralis, m. temporalis, m. sternocleidomastoid, pros. mastoideus, m. trapezius and the insertions of the neck muscles at the base of the scull.) The sum of the individual scores make up the total tenderness.

The stiffness is measured in terms of the speed of the shear waves (meter/second) the higher the speed the stiffer the muscle.

Aided by a palpometer a pressure of 160 U is applied to four different locations (m. masseter, m. sternocleidomastoid, the lateral part of m. trapezius and the medial part of the m. trapezius.) At each location the patient report the pain intensity on a scale from 0-10.